Hi ,
I assume you are using this for cataloguing. I don't use white undercoating
at all in cataloguing. I simply use white ink with the readily available
clear B-72 as a top and bottom coat protecting the artifact.
A good white ink to use is called PEN-OPAKE. Its a white watercolor "ink"
that I get at the local art supply shop.
Regards!
Al Muchka
Associate Curator
American & Local History
Milwaukee Public Museum